Hindfoot Arthrodesis for Pes Planus Correction: Tips and Tricks

Hindfoot arthrodesis offers powerful correction for many deformities. This article will discuss a step-by-step approach to surgically correct pes planus, mainly focusing on double (subtalar and talonavicular joint) arthrodesis. I will also discuss when it is necessary to add calcaneocuboid joint arthrodesis.

I typically reserve the double arthrodesis for rigid flat feet and those patients with a large body mass index (BMI); in my hands, I get better correction utilizing arthrodesis for these patients. Imaging and a proper physical exam are extremely important before selecting a procedure. One should obtain standard weight-bearing views of the foot and ankle, along with calcaneal axial X-rays. Advanced imaging such as magnetic resonance imaging (MRI) or computed tomography (CT) can also prove useful to better understand the underlying morphology. In the physical exam, checking for equinus is paramount, as one must address this during the reconstruction. Evaluation of hindfoot range of motion will help one better appreciate the articular integrity of the joints. Typically, these patients will have rigidity in the hindfoot with significant pain coursing over the posterior tibial tendon. These patients may exhibit pain in the sinus tarsi as well, typically due to sub-fibular impingement. A standing exam facilitates an appreciation of the morphology of the patients foot architecture, while a double and single heel raise exam helps assess the severity of the deformity.

Pertinent Pearls in the Operative Procedure

I begin the procedure by addressing the equinus deformity. For gastrocnemius equinus, I perform an intramuscular lengthening, also known as a Baumann procedure. First, one palpates the tibial crest of the proximal tibia, then three fingerbreadths medially, one can palpate the gastrocnemius. In some patients, the surgeon can feel the separation between the gastrocnemius and soleus muscles. Once making the initial incision, one must take care to avoid injury to the saphenous nerve and vein. Finger dissection then takes place down to the muscular fascia. After incising this fascia, finger dissection will separate the gastrocnemius from the soleus muscle. At this time, the locates and transects the plantaris tendon. Next, an anal speculum placed within the incision allows exposure to the anterior aponeurosis (see photos to left). Utilizing a long-handled #15 blade, from medial to lateral, the surgeon incises the aponeurosis while simultaneously providing ankle dorsiflexion. It is important to close the muscular fascia after performing this procedure to prevent herniation of the muscle bellies.

Next, the surgeon makes a 3-cm incision on the lateral side of the subtalar joint, just distal to the fibular malleolus. If it is necessary to access the calcaneocuboid joint, carry the incision distally towards the fourth metatarsal base. It is vital to protect the peroneal tendons in this incision. One now excises Hoke’s tonsil, the soft tissue plug found in the sinus tarsi. At this time, an osteotome assists in initial joint preparation. It is paramount to excise the calcaneofibular ligament. Placement of a lamina spreader within the sinus tarsi (see photos to left) then distracts the joint. If this is unsuccessful, further evacuation is necessary. Ensure excision of the talocalcaneal ligament. A rongeur is useful to debride the joint. Place the lamina spreader back into the sinus tarsi to distract. Next, a combination of osteotomes, scoop curettes, and ring curettes allow one to resect the cartilage in the posterior facet. Move the lamina spreader within the posterior facet to allow preparation of the middle and anterior facets. To ensure successful fusion, I prepare all three facets and not just the posterior facet.

Once denuding the joint, one irrigates to remove cartilage debris. Leftover debris can hinder reduction and put the joint at risk for nonunion. Next, subchondral drilling takes place with a 2.0-mm drill bit. This allows rich, cancellous bone to come to the surface and increases the surface area of the fusion site. If prefer the drill bit to a Kirschner wire so as to avoid bone necrosis. No further irrigation is advisable, as this will wash away the cancellous bone. To further enhance the fusion site, I perform fish scaling. While this is possible with an osteotome and mallet, I prefer to use a sagittal saw for efficiency.

To access the talonavicular joint, one can use many different incisions. I utilize an oblique incision just medial to the tibialis anterior tendon, beginning at the level of the ankle joint and taken just distal to the navicular tuberosity. This incision gives the surgeon superior exposure to the entire talonavicular joint. This incision warrants care to avoid injury to the saphenous vein. Upon gaining excess to the joint capsule, I perform a capsulotomy with a Bovie cautery device (see photos to left). This allows creation of a flap with the periosteum while simultaneously cauterizing bleeders. A key elevator further extends the flap and gains access to the joint. One should remain aware of the depth of one’s dissection, as the deep peroneal nerve and deep peroneal artery lay dorsal to the talonavicular joint. Joint preparation here is similar to that for the subtalar joint. A lamina spreader distracts the joint, or one may use a pin distractor. 

Key Steps in the Correction: What You Should Know

I correct the subtalar joint first, placing my thumb within the sinus tarsi and pulling the calcaneus forward (see photo). Simultaneously, I place the heel into varus. Next, the other hand or assistant drives a guide wire for a 6.5/7.0-mm headless, partially-threaded cannulated screw into the dorsal talus and through the posterior facet. The talus has a notch just proximal to the neck and just distal to the body where this wire is placed. This maneuver allows reorientation of the talus back on top of the calcaneus and corrects the hindfoot valgus. Fluoroscopic AP ankle, lateral foot, and calcaneal axial views ensures appropriate placement. Before definitive fixation, I reduce the talonavicular joint by placing my thumb on the medial side of the talar head and pushing it laterally to reduce peritalar subluxation. With my other hand, I rotate the forefoot into slight valgus to correct any forefoot varus that becomes unmasked.

Engaging the Windlass mechanism and holding the correction, I place a guide wire for a 5.0-mm headless screw from the navicular into the talus. Alternatively, in deformities with severe peritalar subluxation, one may correct the talonavicular joint first, followed by the subtalar joint. Fluoroscopy confirms appropriate placement of the guidewire.

Definitive fixation placement across the subtalar joint should include care to not fracture the fragile navicular tuberosity. Lastly, I place a dorsal neutralization plate over the talonavicular joint. When performing a double arthrodesis, I do not routinely use two screws in the subtalar joint. However, one may choose a second screw placed from the back of the calcaneus, if desired.

One assesses deformity correction by simulating weight-bearing, including evaluation for any residual forefoot varus. If the surgeon identifies forefoot varus, they may elect to perform a calcaneocuboid joint arthrodesis, lifting the lateral column to balance the forefoot. Final fluoroscopy images check the appropriate placement of hardware. This technique guide did not discuss the use of biologics or autograft, but I do routinely utilize some form of biologic to aid in arthrodesis.

Postoperative Points to Remember

I place a well-padded posterior splint for 3 weeks. Upon suture removal, I advise non-weight-bearing in a CAM boot for an additional 4 weeks. At the 7 to 8 week mark, the patient may partially weight-bear within the boot and begin low-impact physical therapy. At week 10 to 12, the patient will transition to normal shoe gear with use of an ankle brace. Once the patient is fully weight-bearing and has completed physical therapy, I fabricate a custom orthotic.

To conclude, performing a thorough joint preparation for arthrodesis is extremely important to minimize nonunion. The surgeon should check fixation on fluoroscopy including an AP ankle and calcaneal axial view to ensure good placement of hardware. Lastly, the surgeon should check for residual forefoot varus.

Dr. Wadehra is an Associate of the American College of Foot and Ankle Surgeons and a fellowship-trained foot and ankle surgeon with Insight Orthopedics in Detroit, MI. Readers can follow him on Instagram @dr.wadehra for interesting cases.